Obstetrical forceps are almost universally used where it becomes necessary to apply tractive force to the fetus during childbirth. Heretofore, nearly all obstetrical forceps were manufacturing from unyielding materials, such as stainless steel. When such rigid material is engaged against the soft, moldable fetal head, undesirable and potentially damaging compression can occur. This, of course, is an inherent drawback in the use of such forceps, and the avoidance of the inherent dangers associated with use of forceps on the fetal head has been a matter of constant concern. A faulty application or incorrect use of the forceps will not only injure the fetus, but can also cause maternal injuries as well. Since present day obstetrical training programs tend to de-emphasize the use of forceps, it can no longer be assumed that those who infrequently use forceps will be thoroughly proficient in their use, increasing the danger that either fetal or maternal injuries are likely to follow.
Investigations have clinically and experimentally measured the compression and tractive forces applied in the use of obstetrical forceps. An average compression force on the fetus' skull of 20 kg. has been generally observed as being the approximate threshold level of force below which forceps would not likely produce injuries to the fetus, while above which injury was likely to occur. In general, the average compressional force applied to primigravidas was approximately 18 kg., and in multi-pares 13 kg. The delivery pressure of the uterine muscles was recorded at 4.2 kg., increasing to around 9 kg. with expulsive efforts.
Faulty application of the forceps can result in elevation of the tentorium and displacement of the faix, which can become excessive with tear, and can be followed by subcortical and cortical bleeding or sinus rupture. The sagittal sinus can also end up congested and dilated, and the brain stem angulated. It has been observed that fetal electroencephalograms show rapid change from low voltage to irregular activity to even flat line recordings after forceps application. Such irregular activity was not seen in spontaneous deliveries. Further, fetal heart rate was found to vary in relation to the fetal head compression.
Initial application of the forceps is usually for the purpose of converting an unfavorable presentation to a more favorable one by rotating the fetus in the birth canal. Once in a proper presentation, the forceps are then used to apply tractive force to the fetal head and thereby assist in delivery by effectively pulling the infant through the birth canal.
Besides the already noted problems related to unyielding compression of the fetal head, forceps also are subject to friction between the outer surface of the forceps and the birth canal, which adds to the tractive forces which must be applied for successful delivery.
The concept of using a constricting net for tractive delivery of a fetus is not new in the art, as shown by U.S. Pat. No. 13,453 and 713,166. Both of these patents show a resilient net or web which is placed around the fetal head in utero through the use of rigid blade members. Once in place surrounding the fetal head, the free net end can be grasped and pulled to effect rotation and/or delivery. Such tractive nets have the advantage that the compression force applied to the fetal head is more evenly distributed.
As will be more clearly shown in relation to the instant invention, both of the foregoing nets disadvantageously employ rigid blades to position the net, and neither net features a mesh which ruptures at a predetermined excessive force.